This invention relates to a blade mechanism for use in a focal plane shutter for a camera.
In general, in the so-called metal focal plane shutter mechanism which is opened and closed to varying degrees by coordinated displacement of a plurality of separate shutter blades by means of a shutter operating member, the individual shutter blades normally must be made relatively large in conformity with the wide shutter aperture opening area. This requires an increased shutter space and is disadvantgeous for compact cameras. Especially, in the recently popular single lens reflex camera employing the metal focal plane shutter of the type wherein the image to be photographed is viewed through the photographing lens by use of a viewfinder arranged on top of the camera body, the shutter blades are retractable within the camera body at an upper position and are disposed directly below the viewfinder thereby limiting the vertical position of the viewfinder and thus preventing miniaturization of the camera. In other words, the bottom portion of a single lens reflex camera of this type is determined by the size of either the film chamber or the lens tube; while the top portion is defined by the position of either the pentaprism or viewfinder. The lower portion of the camera will therefore have almost constant dimensions and may be used comparatively efficiently as a space for receiving the shutter. However, one of the most important conditions for making the camera compact is to reduce the space for receiving the shutter blades which are retractable between the shutter aperture and viewfinder. This disadvantage, which is not encountered in the focal plane shutters of the type wherein the shutter curtains are forced to run sidewardly, has been the greatest disadvantage of focal plane shutters of the type wherein the separate metallic blades are forced to run in the vertical direction.
This invention intends to eliminate the foregoing disadvantages by providing a blade mechanism for use in a focal plane shutter which is suitable for compactizing the camera. This purpose is attained by efficiently using the space within the camera body to accommodate the shutter blade mechanism.
The shutter mechanism of the invention dispenses with the conventional need of employing an equal number of or similarly shaped opening blades and closing blades and instead, the group of opening blades which are retractable within the camera body at the lower position may be composed of, for example, three separate blades so as to effectively utilize the lower space defined within the camera body and thus reduce the cost of the camera.
On the other hand, the group of closing blades which are to be retractable within the camera body at the upper position may be composed of four or five small-sized blades so as to minimize the blade-receiving space defined in the camera body at the upper position so that the viewfinder may be arranged at a closer position to the shutter aperture. By these means, the invention makes it possible to provide a focal plane shutter which is suitable for use in a compact camera and presents a fully effective light-shielding property.
Furthermore, of the group of blades to be folded up or retracted within the camera body at an upper position, the blade portions which are disposed within the region defined vertically by the viewfinder may be made smaller in width along the extent of the viewfinder than the blade end portions which are not situated vertically beneath the viewfinder. As a result, it may be possible to increase the longitudinal dimension of the shifting pivot shaft for the slit-forming blades. This contributes to the stabilization of the width of the slit during an exposure operation and to the arrangement of the viewfinder at a closer position to the shutter aperture without adversely influencing the film exposure, whereby a focal plane shutter suitable for use in a more compactized camera can be obtained.